Scientists admit they still baffled by SARS

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Three months into the global outbreak of SARS and scientists admit they are still baffled by the new disease, which is like so many other respiratory ailments - and yet so different.

The re-emergence of the scourge in Toronto - which had been thougth cleared - showed just how difficult the virus was to beat.

"We have seen how complacency can lead to the re-emergence of this disease," Dr Klaus Stohr, leader of the SARS team at the World Health Organisation, told a conference in Bethesda, Maryland arranged by the U.S. National Institutes of Health.

Doctors know that Severe Acute Respiratory Syndrome kills about 15% of patients, that the incubation period is between five and 10 days (with some exceptions), and that people do not seem to transmit the infection to others until they develop symptoms.

They also know it is also transmitted by droplets through coughing, and that the virus may also linger on surfaces, waiting to be picked up and rubbed into an eye, nose or mouth, and the possibility remains that it can become airborne. Bits of the virus can be found in the stool, urine, tears and saliva of patients. But no-one knows if these play a role in spreading the disease.

And while children have become infected, they do not seem to spread it - unlike many other viral diseases from the common cold to influenza, measles and chickenpox. "What role do children play?" Stohr asked delegates to the meeting.

While SARS is defined as a respiratory disease and is caused by a relative of a new type of coronavirus - a group that causes one-third of common colds - its symptoms are not always obvious.

Dr Allison McGeer, director of infection control at Toronto's Mount Sinai Hospital, said at one point in Canada's outbreak, "at least half" of patients later found to have viral infections were sent home with useless antibiotics. The only symptom that all SARS patients have is fever, which is a hallmark of hundreds of other diseases. McGeer said her team found only 10% have a runny nose.

Only 29% of SARS patients McGeer's team studied had a cough. Pneumonia often does not show up on an X-ray until people have been sick for a week - long enough for them to spread this disease to many others. There are several tests for SARS, but all are experimental and unreliable. One can only be given 21 days after infection - useless for controlling the spread of disease.

Most puzzling has been the death rate. "This is a slowly progressive disease," McGeer said. "We are used to seeing the greatest mortality right away ... that is not true of SARS. Mortality peaks at day 15 to 17. It takes four, five, six, seven weeks for some people to die."

Also puzzling is why some people seem able to infect dozens of others at one fell swoop, and others infect no one else. "In the early stages of the outbreak, we were pretty cavalier about saying if you don't have pneumonia, go home and spend time in isolation," said Dr Donald Low, McGeer's colleague at Mount Sinai.

"People were going to malls, they were going to saunas and trying to sweat out the fever, but it was not spread in the community. What this says is that this is not a good virus for transmitting outside certain settings."